There are only two situations to investigate the problem, and there are two changes in each situation. As long as we firmly grasp these two situations, we can easily solve the catch-up problem.

1, introduction of questions

Catch-up problem is a typical application problem of travel problem, and it is also a problem of studying "same direction movement". The catching-up problem reflects the relationship between distance, speed and travel time between two or more quantities. The core is the speed difference.

2. Core knowledge

Catch-up time = distance difference ÷ speed difference;

Distance difference = chasing time × speed difference;

Speed difference = distance difference ÷ pursuit time.

Xiaohong and Xiaoming's homes are 300 meters apart. They both left home for school at the same time. Xiaoming is behind Xiaohong, and Xiaoming scores every point.

Clock walking160m, Xiaohong walking every minute100m. How many minutes does Xiaoming catch up with Xiaohong?

Catch-up time = distance difference/speed difference = 300/( 160- 100) = 5 minutes.

3. A detailed description of the use of core knowledge

When the catching-up problem occurs in a straight line: distance difference = chaser distance-chased distance = speed difference × catching-up time;

When it happens on a circular path: fast path-slow path = the circumference of the curve;